A. After December 31, 1994, a person may enter into a contract to make a will or devise or not to revoke a will or devise or to die intestate only by:
1. Provisions of a will that state the material provisions of the contract.
2. An express reference in a will to a contract and extrinsic evidence proving the terms of the contract.
3. A writing signed by the decedent evidencing the contract.
B. The execution of a joint will or mutual wills does not create a presumption of a contract not to revoke the will or wills.